It is known that calcium, the most common mineral in the human body, is found as a calcium phosphate salt mainly in bones and teeth, and thus is important to maintain bone strength. Particularly, a trace amount of calcium present in blood and cells has important metabolic effects, such as regulation of cardiac rhythm, activation of muscles and nerves, blood coagulation, and increases in enzymatic activity and cell membrane permeability.
Because more than 99% of the human body's calcium reserves are stored in bones and teeth, calcium is important for bone growth and formation and during the lactation period. Specifically, for infants, adolescents, and pregnant and nursing women, calcium intake is very important, and foods and various supplements are used to meet the recommended daily calcium intake. Thus, calcium-containing products, including calcium-containing foods, drugs and quasi-drugs, have been actively developed.
The absorption of calcium is greatly influenced by dietary components and in vivo factors. Dietary components that can be externally controlled include vitamin D, lactose, protein, amino acid, lipid, phosphoric acid, the calcium-to-phosphorus ratio, oxalic acid, and the like. Among them, protein, lipid, phosphoric acid and oxalic acid interfere with the absorption of calcium when they are taken in excessive amounts, whereas vitamin D, lactose and amino acid help the absorption of calcium. Particularly, it is known that the absorption rate of calcium is good when the molar ratio of calcium and phosphorus is 1:1 to 2:1, because this ratio is similar to the calcium-to-phosphorus ratio of a calcium phosphate-based compound forming the bone of the human body.
When supplements other than foods are used to take calcium, the intake of calcium can vary depending on the formulation of the supplements, rather than depending on dietary components. Calcium supplements that are in common use are prepared in the form of tablets which take 4-6 hours to dissolve in the body. When calcium supplements are prepared as capsules, the supplements dissolve more easily than calcium supplement tablets and are more easily absorbed into the body. In other words, because the rate of absorption of calcium into the body has a great significance, whether calcium was prepared in a form which can be easily absorbed into the body after intake can be considered as an important factor.
Meanwhile, it is well known that tooth hypersensitivity occurring die to damaged teeth can be relieved by remineralization using a calcium phosphate compound. Specifically, tooth hypersensitivity is relieved by treating dentinal tubules, exposed due to the decalcification of teeth enamel, with hydroxyapatite, and this relief can be achieved by precipitation of an aqueous solution containing a high concentration of calcium phosphate.
With respect to the requirements of an aqueous calcium phosphate solution for tooth remineralization, the aqueous solution should form a precipitate on the tooth surface when applied to the tooth, and the stability of pH and ions of the solution should be well maintained during storage.